diff --git a/scripts/upgrade b/scripts/upgrade
index 420dbcc..880799f 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -25,6 +25,12 @@ ynh_systemd_action --service_name=$app --action="stop" --log_path="/var/log/$app
 #=================================================
 ynh_script_progression --message="Ensuring downward compatibility..." --weight=1
 
+if [ -z "${public_key+x}" ]; then
+    # Missing setting ?
+    public_key=""
+    ynh_app_setting_set --app="$app" --key=public_key --value="$public_key"
+fi
+
 #=================================================
 # INSTALL NODEJS
 #=================================================